The market of artificial leathers formed from extremely fine synthetic fibers such as polyester fibers has heretofore been enlarged in applications such as clothing, family furniture and seats for vehicles because they have a good surface appearance, a good feel that is soft and swollen, easy handleability and provide fastness of various types. However, there have been restrictions on using the artificial leathers for applications that require the artificial leathers to have flameproof properties due to the poor self-extinguishability that is a disadvantage of synthetic fibers.
In order to solve the problems, it has been usual to make the synthetic fibers flameproof by making the synthetic fibers contain halogen compounds, containing chlorine or bromine as a main component, or antimony compounds. However, synthetic fibers having been made flameproof by such a method have problems that the compounds themselves, contained in the fibers, have toxicity and that there is fear of generating dioxin during incineration. Accordingly, there is a tendency to restrict the use of such compounds.
Japanese Examined Patent Publication (Kokoku) No. 3-80914 and Japanese Unexamined Patent Publication (Kokai) No. 5-302273 disclose a method of back coating with a flame retarder as a technology for giving flameproof finish to an artificial leather with a suede finish. The method has been developed principally for seats for vehicles and seats for aircraft. The artificial leathers thus obtained have a rough and stiff feel. They are unsatisfactory to the touch and, moreover, show insufficient stretchability. The artificial leathers therefore have the disadvantage that they show inadequate workability when used for products having complicated shapes. Furthermore, when the artificial leathers are back coated with a flame retarder, they each show a weight increase of 100 g/m2 or more. The method is therefore undesirable for automobiles that use many lightening technologies.
There is a method of impregnating an artificial leather in a finishing step after dyeing with an organic phosphorus type flame retarder that does not generate a harmful gas and has good flameproof properties. However, the phosphorus type flame retarder is generally water soluble, and has poor affinity with the fiber. The flame retarder therefore easily leaves the fiber when waterdrops stick to the fiber and, as a result, the artificial leather shows a deteriorated flameproof finish. Moreover, when a large amount of the flame retarder is made to adhere to the fiber in order to increase the flameproof properties, not only does the artificial leather have a sticky feel on the fiber surface, but also the dye is likely to bleed. The colorfastness of the artificial leather is likely to be low.
There is an effective method for a flameproof finish in specific applications. For example, Japanese Unexamined Patent Publication (Kokai) No. 2002-38374 discloses an artificial leather to be used for CD curtains or the like. According to the patent publication, in order to satisfy the self-extinguishability in accordance with JIS D-1201 of an artificial leather for which a synthetic fiber is used, and prevent at the same time falling of the liquid drops, the flame retarder described in the patent publication must be imparted in an amount of 40% by weight or more. When an artificial leather to which the flame retarder is imparted in such a large amount, the artificial leather has a sticky feel on the surface, and the feel becomes poor. However, use of the artificial leather in a part human hands substantially do not touch, for example, a CD curtain used in the interior of a CD drive, causes no problem.
Japanese Unexamined Patent Publication (Kokai) No. 7-18584 discloses a method of mixing a flame retarder with polyurethane. Because the resultant polyurethane resin has a lowered resistance to light, the artificial leather cannot withstand be used for seats for vehicles that are required to have a particularly high resistance to light. In general, when a method of adding a flame retarder to a polyurethane is employed, making the flameproof properties and the resin properties compatible is difficult.
Japanese Unexamined Patent Publication (Kokai) No. 2002-105871 discloses a method of making fibers exhaust a phosphagen compound having a large phosphorus content in a bath also used for dyeing. The most difficult point of the method is contamination of the dyeing machine. When fibers are continuously dyed and exhausted in many batches, the interior of the dyeing machine is contaminated, and many contamination defects are formed on the fibers. Contaminants sticking to the interior of the dyeing machine are hardly removed by simple chemical cleaning, and the contaminants must be removed physically by disassembling and cleaning the dyeing machine. Moreover, because the environmental impact produced by polluted wastewater generated in the course of the removal is high, the industrial practice has many problems.
Japanese Unexamined Patent Publication (Kokai) No. 2004-131875 discloses an artificial leather prepared by filling an integrated material of an extremely fine fiber nonwoven fabric that is formed from a phosphorus copolymerized polyester with a small amount of a polymer elastic material. Japanese Unexamined Patent Publication (Kokai) Nos. 2002-115183 and 2002-294517 disclose an artificial leather prepared by filling an integrated material of an extremely fine fiber nonwoven fabric formed from a phosphorus copolymerized polyester with an aluminum hydroxide-containing polymer elastic material. Moreover, Japanese Unexamined Patent Publication (Kokai) No. 2002-201574 discloses an artificial leather prepared by filling an integrated material of an extremely fine fiber nonwoven fabric formed from a phosphorus copolymerized polyester with an organic phosphorus component-copolymerized polyurethane.
For the artificial leathers disclosed in these references, a phosphorus copolymerized polyester fiber is exposed to the top surface thereof, and is contacted with the external part during the use. Because the phosphorus copolymerized polyester fiber has poor resistances to light and abrasion in comparison with a polyester fiber formed from a homopolymer, exposure of the phosphorus copolymerized polyester fiber on the top surface of the artificial leather becomes an extremely great disadvantage in the application of the artificial leather to seats for vehicles.
In order to solve such a problem, a polyester fiber containing no flameproof component is used in Japanese Unexamined Patent Publication (Kokai) No. 2004-107840. Moreover, as described in Japanese Unexamined Patent Publication (Kokai) Nos. 2002-115183, 2002-294517, 2002-201574 and 2004-107840, when an organic solvent type polyurethane is used as a binder by a wet method, an impregnation amount of as large as 25% by weight or more based on the artificial leather base fabric is necessary.
Because polyurethane burns readily, an artificial leather having a larger impregnation amount of polyurethane becomes more disadvantageous with respect to flameproof properties. Accordingly, use of a polyurethane that is copolymerized with aluminum hydroxide or a phosphorus component has been proposed for the purpose of compensating for the deterioration of the flameproof properties. However, such a copolymerized polyurethane resin is not desirable because it is likely to be embrittled. Moreover, a sheet-like material obtained by applying such a technology has a very large fabric weight and, for example, in a weight of larger than 600 g/m2, the resultant product becomes extremely heavy. The resultant artificial leather is not suited to the application for a seat for vehicles that is desirably lighten, as explained above.
Even when lightening an artificial leather, as described in Japanese Unexamined Patent Publication (Kokai) No. 2004-107840 or the like, by thinning it is tried, sufficient flameproof properties are hardly obtained for the reasons explained below. For artificial leathers having the same composition, an artificial leather having a thinner base fabric has a larger surface area per unit fabric weight to have a larger area to be contacted with the air. As a result, the artificial leather more readily burns because oxygen more readily supplied during burning.
As explained above, a technology capable of industrially and stably providing flameproof artificial leathers of suede finish that have a soft feel, that satisfy the severe requirements for resistances to light and abrasion such as those for seats for vehicles and that are lightweight, has not been developed yet.